Inverting a dictionary in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of simple dictionary inversion

What is the output of this Python code that inverts a dictionary?

Python

original = {'a': 1, 'b': 2, 'c': 3}
inverted = {v: k for k, v in original.items()}
print(inverted)

A TypeError

B {'a': 1, 'b': 2, 'c': 3}

C {'1': 'a', '2': 'b', '3': 'c'}

D {1: 'a', 2: 'b', 3: 'c'}

💡 Hint

Think about swapping keys and values in the dictionary comprehension.

The dictionary comprehension swaps keys and values, so the output maps values to keys.

❓ Predict Output

intermediate

Inverting dictionary with duplicate values

What is the output of this code that tries to invert a dictionary with duplicate values?

Python

original = {'a': 1, 'b': 2, 'c': 1}
inverted = {v: k for k, v in original.items()}
print(inverted)

A {1: 'c', 2: 'b'}

B KeyError

C {'a': 1, 'b': 2, 'c': 1}

D {1: 'a', 2: 'b', 1: 'c'}

💡 Hint

When keys repeat in a dictionary, the last one stays.

Since keys must be unique, the last key for value 1 ('c') overwrites the first ('a').

🔧 Debug

advanced

Identify the error in dictionary inversion code

What error does this code raise when trying to invert a dictionary?

Python

original = {'a': [1, 2], 'b': [3, 4]}
inverted = {v: k for k, v in original.items()}
print(inverted)

A SyntaxError

B No error, prints inverted dictionary

C TypeError

D KeyError

💡 Hint

Dictionary keys must be immutable types.

Lists are mutable and cannot be dictionary keys, so a TypeError is raised.

🧠 Conceptual

advanced

Number of items after inverting dictionary with unique values

If a dictionary has 5 unique keys and 5 unique values, how many items will the inverted dictionary have?

A 10

B 5

C 0

D Depends on the values

💡 Hint

Inversion swaps keys and values one-to-one if all are unique.

Each unique key-value pair becomes a value-key pair, so the count stays the same.

❓ Predict Output

expert

Output of inverting dictionary with tuple values

What is the output of this code that inverts a dictionary with tuple values?

Python

original = {'x': (1, 2), 'y': (3, 4)}
inverted = {v: k for k, v in original.items()}
print(inverted)

A {(1, 2): 'x', (3, 4): 'y'}

B {'x': (1, 2), 'y': (3, 4)}

C TypeError

D {'(1, 2)': 'x', '(3, 4)': 'y'}

💡 Hint

Tuples are immutable and can be dictionary keys.

Tuples can be used as keys, so the inversion works and swaps keys and tuple values.